1. Technical Field
The present invention relates to a fixing unit and an image-forming device for fixing toner images that have been transferred onto a paper or other recording medium.
2. Description of the Related Art
Conventionally, electrophotographic image-forming devices, such as laser printers, are equipped with a light-emitting unit including a laser diode for emitting a light beam, and a photosensitive member, the surface of which carries a uniform charge. When the surface of the photosensitive member is exposed to the light beam, electrostatic latent images are formed on the surface of the photosensitive member and the latent images are then developed into visible images with toner. Subsequently, the visible images are transferred onto a paper or other recording medium to form visible toner images thereon.
However, the images transferred onto the recording medium are merely carried to the recording medium by an electrostatic force or dispersion force at this time and can be easily removed from the recording medium. Therefore, a fixing process is required to fix and attach the visible images to the recording medium through a step of applying heat.
A fixing device provided in the image-forming device for fixing images using heat typically includes a heating roller and a pressure roller. As the recording medium passes between the heating roller and the pressure roller, the toner or other developing material is sintered and coalesced by the heat from the heating roller, so as to permeate and become fixed to the recording medium. The heating roller accommodates a heat source, such as a halogen lamp. Since failure if the halogen lamp is fatal to the image-forming device, resulting in a loss of the fixing function, the fixing unit must be configured in such a way as to be easily replaceable. Japanese patent application publication No. HEI 8-305205 discloses a fixing unit integrally configured of a heating roller and a pressure roller that can easily be replaced when malfunctions occur.
Further, in order to prevent the heating roller from rising to an abnormal temperature due to a failure of the heating source, the fixing unit is provided with a temperature fuse that interrupts the supply of power to the heating roller when the surface of the heating roller reaches an abnormal temperature.
Normally, the temperature fuse is fixed to contact points provided on a main fuse body by a synthetic resin disposed around the contact points in order to electrically connect these points. Upon reaching a prescribed fusing temperature, the resin melts, causing a spring provided in the fuse to break the connection between contact points and halt the supply of power. Since the temperature fuse is connected to the power source in this case, the temperature fuse is required not to electrically contact the heating roller. Normally, safety standard for electronic equipment (explosion-proof construction standards for general electronic equipment) stipulate that a distance of at least 4 mm should be maintained between the fuse and heating roller as an insulating distance.
Proposals have been made for technologies that interpose a fuse cover between the heating roller and the temperature fuse so as to reliably insulate the two. For example, Japanese patent application publication No. HEI 9-281842 discloses a fixing unit in which a temperature fuse is attached to the underside surface of an electrically insulated member having a heat collecting surface opposing the heating roller.
In Japanese patent application publication No. HEI 9-281842, the fuse cover is provided as a separate member. After the temperature fuse is attached to the fuse cover, the fuse cover is mounted in the fixing device. This assembling way may increase a cost of the image-forming device.
Further, the fixing unit of Japanese patent application publication No. HEI 8-305205 strictly regulates the relationship between the position of the fuse on the fuse cover and the fixing device. Accordingly, the fuse cover is not sometime appropriately mounted in the fixing device if there is any variation in the lengths of the leads on both ends of the temperature fuse.